HYPOCHLORITE OF LIME.

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Preparation. —It is prepared by conveying chlorine gas into a vesselor chamber containing slacked lime. On the large scale the gas is gene-rated in large, nearly spherical, leaden vessels heated by steam. Theingredients employed are binoxide of manganese, chloride of sodium,and diluted sulphuric acid. The gas is washed by passing it throughwater, and is then conveyed by a leaden tube into the combination room,where the slacked lime is placed in shelves or trays, piled over oneanother to the height of five or six feet, cross bars below each, keepingthem about an inch asunder, that the gas may have free room to cir-culate. The combination room is built of siliceous sandstone, and isfurnished with windows, to allow the operator to judge how the impreg-nation is going on. Four days are usually required, at the ordinary rateof working, for making good marketable chloride of lime (Ure, Quart.Journ. of Science, xiii. 1). At Mr. Tennant’s manufactory at Glasgow ,the lime is placed in shallow boxes at the bottom of the combinationchambers, and is agitated dining the process by iron rakes, the handlesof which pass through boxes filled with lime, which serves as a valve(American Journ. of Science, vol. x. No. 2, Feb. 1826, and Dumas’ Traitede Chimie, ii. 806). The theory of the process will be noticed whendescribing the composition of this substance.

Properties. —Chloride of lime, as met with in commerce, is a whiteor brownish white powder, having a feeble odour of chlorine, and a strongbitter and acrid taste. Exposed to the air it evolves chlorine, and at-tracts carbonic acid, and is thereby converted into a mixture of carbonateof lime and chloride of calcium, the latter of which deliquesces. Digestedin water the chloride or hypochlorite of lime dissolves, as well as anychloride of calcium present, and a small portion of caustic lime : any car-bonate and the excess of caustic lime remain undissolved. The solution,which has a slight yellow colour, first reacts on vegetable colours as analkali, and afterwards bleaches them. Its bleaching and disinfecting pro-perties depend on the oxidizement of the colouring or infectious matter: ifan acid be employed in the process, chlorine is evolved, which producesoxygen at the expense of the elements of water, as before mentioned(p. 107) : if, on the contrary, no acid be used, Balard ( Researches, inTaylor’s Scientific Memoirs, vol. i. p. 269) supposes that both the hypo-chlorous acid and lime give out their oxygen, and thereby become chlo-ride of calcium. When chloride of lime is heated it evolves first chlorineand subsequently oxygen.

Characteristics. —Its smell and bleaching properties are most cha-racteristic of it. The acids (as sulphuric or hydrochloric) separate chlo-rine from it. An aqueous solution of it throws down white precipitateswith nitrate of silver, the alkaline carbonates, and with oxalic acid or theoxalates. The supernatant liquor from which chloride of silver hasbeen thrown down by nitrate of silver possesses a decolorizing property.

Composition. —Chemists are not agreed as to the nature of the sub-stance called chloride of lime. By most English chemists (Dalton,Thomson, Brande, Turner, and Phillips), it is supposed that when chlo-rine comes in contact with slacked lime combination takes place, and thatthe lime undergoes no decomposition. By others (Berzelius , Souberain,and Balard), however, it is supposed that part of the lime is decomposed;one portion of the chlorine uniting with the calcium to form chloride ofcalcium, and another with the oxygen to become hypochlorous ( chlorous ,